1. Field of the Invention
The present invention relates to the control of a spindle motor in a disk drive system. More particularly, the present invention relates to the control of the spindle motor in a disk drive system.
2. Art Background
Disk drives are popular peripherals for the storage of data. A number of different types of disk drives and media exist such as hard disk drives, floppy disk drives and optical drives. The disk containing the media on which the data is written to and read from is mounted to a spindle. The spindle and disk must be rotated at a precise, nonvarying speed in order for the head assembly, which is positioned above the surface of the disk, to read and write data on the disk surface. The spindle rotation is controlled by a spindle motor. In order to control the spindle motor, a signal, typically referred to as the commutate signal, is generated by control circuitry. Optimally the commutate signal is generated at a point and time which corresponds to a halfway point between transitions of the back EMF signal (BEMF) which transitions or toggles between a logic 1 and logic 0 state as the spindle motor spins and is therefore synchronized to the revolutions of the spindle motor such that there are multiple transitions per revolution of the spindle motor. The period between BEMF transitions is proportional to the speed of the motor and thus varies as the motor accelerates or decelerates.
The commutate signal should therefore be centered between transitions of the BEMF signal regardless of the time interval between BEMF transitions, i.e., the speed of the motor. The centering of the commutate signal is important for both power efficiency of the spindle motor and the smooth control of spindle speed.
The commutate signal is typically generated in one of two ways. In one method, an analog signal is generated using external passive components and analog circuits. This is a costly method due to the costs of providing the additional external circuit and components for each drive. In an alternate method, the disk drive controller (microprocessor) is used to generate the commutate signal. This method requires a commitment from the controller's microprocessor to perform real time processing in order to timely generate the commutate signal. As the controller provides a multiplicity of functions, real time processing to generate a commutate signal increases the processing complexity and causes either a reduction of performance in the other disk drive functions or a requirement that the controller's microprocessor be more powerful and therefore more complex and costly.
The circuit of the present invention generates the commutate signal using simple digital circuits that are easily implemented, in pre-existing real estate of a digital ASIC (Application Specific Integrated Circuit) component. Thus, one value of this invention is that it can be implemented in a digital ASIC component and provides an inexpensive solution that does not impact the performance of the disk drive.